For TNB customers, you can now apply for tariff change online, via myTNB portal. Yes, it is only available on their website portal, not on the app yet.

These are the steps:

myTNB portal > Apply > I want to do something else > I want to find out more about other services > Select your TNB account and click "next" > Change my tariff.

You will need to upload your proof of identity too.

Good luck!